Coffee makers can be generally divided into three types according to the way they used to brew coffee, namely, a siphon coffee maker, an Espresso coffee maker, and a drip coffee maker. The siphon coffee maker is also referred to as a vacuum coffee maker and basically includes two ball-like glass chambers with one fitted to a top of the other one, and the two glass chambers are separated from each other by a strainer having a filtering cloth fixed thereto. To brew coffee, first fill the lower glass chamber with boiled hot water, and then fix the upper glass chamber and the strainer to the top of the lower glass chamber. Thereafter, pour ground coffee beans into the upper glass chamber, and heat the water in the lower glass chamber using an alcohol lamp or other heat source. When the water is boiled, vapor pressure is produced in the lower glass chamber to force the water through a narrow tube into the upper glass chamber to contact with the ground coffee beans. Through stirring, the hot water mixes with the ground coffee beans to absorb the aroma and four flavors of coffee. After the ground coffee beans are sufficiently brewed with water, the heat source is removed. When the air in the lower glass chamber is cooled, the resulting vacuum will draw the brewed coffee through the paper filter back into the lower chamber. At this point, the brewed coffee with aromatic smell and good flavors can be poured into a preheated cup for drinking.
In Espresso brewing, finely ground coffee beans with uniform size are compacted with a compacting tool, so that the ground coffee beans in the filter must be in the form of a compacted cake of coffee to resist the very hot water forced under high pressure through the finely ground, compacted coffee. When the cake of coffee has uniform compactness, all granules of the ground coffee beans are evenly and completely extracted by the hot water to make a cup of concentrated and aromatic Italian Espresso coffee. A balanced symmetry between the water pressure and the resistance of the compacted cake of coffee to the water pressure forms an important and prerequisite factor to brew a cup of high quality Espresso coffee. Since the Espresso brewing means the use of an adequate pressure to force hot water quickly through the ground, compacted coffee beans, only 25 to 30 seconds are needed to extract a cup of coffee to largely save the time and cost of brewing coffee.
In drip brewing, as suggested by its name, a strainer is fixed to a top of a vessel, and a paper filter is put over the strainer. Ground coffee beans are poured on the paper filter and hot water is poured into the strainer, so that the hot water seeps through the ground coffee beans and passes through the fine holes at the bottom of the strainer to drip into the vessel to make a cup of fresh and aromatic coffee. The drip brewing is characterized in that the hot water is sufficiently mixed with the ground coffee beans to extract the aroma and special four flavors of coffee. The extracted liquid of coffee passes through the paper filter and drips into the vessel. Brewing with a paper filter produces clear, light-bodied coffee, which is free of fats, proteins and undesired impurities, allowing people to enjoy delicious coffee without endangering their health.
One of the most important skills for the drip brewing lies in good control of the volume and stability of water poured into the ground coffee beans. By stably pouring adequate volume of hot water in a spiral rotational course from a central point to outer and inner areas of the paper filter in a reciprocating motion, the ground coffee beans can be evenly extracted and all the aroma and flavors of the ground coffee beans can be fully released into the hot water. However, the drip brewing process is usually manually performed, and the experience of the coffee brewing person forms a major factor in brewing a good cup of drip brewed coffee. A person lacking sufficient experience in drip brewing often fails to evenly and reciprocatingly pour the hot water on the ground coffee beans in the spiral rotational course, and as a result, the extracted liquid of coffee dripped into the vessel or the cup is not smooth to adversely affect the overall flavor or taste of coffee. In view that the quality of the manually drip brewed coffee is largely subjected to the experience of the brewing person, it is necessary to develop a coffee maker that enables automated drip brewing in a mass-production manner without being influenced by the experience of an operator.